Physics

7.6 - Components

5 min

Circuit symbols

Meters and resistors

LDRs and thermistors

note 1 of 2

Light-dependent resistors (LDRs)

A light-dependent resistor (LDR) is a resistor whose resistance depends on the intensity of light falling on it.
In darkness, its resistance is highest.
As the light gets brighter, its resistance falls.
Common applications: automatic night lights, outdoor lighting, and burglar detectors.

note 2 of 2

A thermistor is a resistor whose resistance depends on temperature.
In cold conditions, its resistance is high.
As the temperature rises, its resistance falls.
Because resistance falls as temperature rises, it's called a negative temperature coefficient (NTC) thermistor.
Common applications: car engine temperature sensors, thermostats, irons, and fire alarms.

key terms

TermDefinition

Light-dependent resistor (LDR)A resistor whose resistance decreases as the intensity of light falling on it increases.

ThermistorA resistor whose resistance decreases as its temperature increases.

end of notes